Late Quaternary environmental change and ecological response along the Sumatra-Java-Flores transect in tropical SW and S Indonesia
Final Report Abstract
The marine core BAR94-42 southwest Sumatra, the core GeoB 10053-7 west Java and GeoB 10069-3 Flores, taken offshore in the Indian Ocean have been studied by pollen analysis. The objectives of the project are the investigation of terrestrial environmental dynamics and marine current changes in tropical SW and S Indonesia on a transect from the Islands Sumatra, Java to Flores. The new pollen and re-interpreted biogenic and terrigeneous data from core BAR94-42 were used to reconstruct monsoon circulation and vegetation of southwest Sumatra over the last 83,000 years (83 kyr). During marine isotope stage (MIS) 5a, southwest Sumatra was covered by rainforest, with open herbaceous swamps lining river courses and surrounding lakes. The SE component of the monsoon was stronger than the NW component, resulting in a humid climate with a short, dry season. During MIS 4, conditions were drier, fire activity increased and the monsoon was generally weaker. This latter pattern persisted until MIS 1. The vegetation was most open during MIS 3, between ~52 and 43 kyr; identifying this phase as the driest of the last glacial. An increase in montane trees from ~ 52 kyr indicates the onset of cooler conditions, which lasted until the transition to MIS 1 at about 11.9 kyr. After ~43 kyr, an everwet climate gradually developed as monsoonal circulation intensified and the SE monsoon component became stronger. During this time, closed-canopy rainforest became dominant regionally over southwest Sumatra. Increased monsoonal activity during the early Holocene resulted in increased precipitation, river runoff, sediment discharge and offshore sediment transport from the continental shelf. The palynological results from cores GeoB 10053-7 and GeoB 10069-3 indicate much more open vegetation forms (savanna) with some forest vegetation in the southern part of the transect during glacial times. The climate was much drier than in the northern part (Sumatra) of the transect and the dry season must have been much longer than today. At least since the beginning of the Holocene open vegetation forms have been replaced by different forest types. The human impact was probably much stronger in East Java than in the Flores region during the late Holocene. The occurrence of mangroves were relatively stable during the recorded period, except the high frequency at the end of glacial period and the early Holocene in East-Sumatra. The overall studies indicate that the ecological response to environmental change was different along the Sumatra – Flores transect. The investigation of dinoflagellate cysts on a large set of marine surface samples document the occurrence of the three dominant dinocysts species in the eastern Indian Ocean. This seems to be tied to specific water masses, namely the North Indian waters, the Indonesian Throughflow and the South Indian Central Waters. Based on the dinocyst composition of the surface samples statistical analysis reveals the existence of two environmental gradients (temperature, nutrients) in the study area. The core-samples can also be attributed to five distinct geographical regions.
Publications
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2010. Changes in monsoon and ocean circulation and the vegetation cover of southwest Sumatra through the last 83,000 years: The record from marine core BAR94-42. Palaeogeography, Palaeoclimatology, Palaeoecology, 296: 52–78
van der Kaars, S., Bassinot, F., De Deckker, P., Guichard, F.
